Reduce misconceptions about Cursor being more general than it really is.

Fixes: rust-lang#52470

Instead, rely on alignment and use usize::MAX as sentinel.

Since NonNull is Copy the inner field of the cloned Waker was copied for
use in the new LocalWaker, however this left Waker to be dropped. Which
means that when cloning LocalWaker would also erroneously call drop_raw.

This change forgets the Waker, rather then dropping it, leaving the
inner field to be used by the returned LocalWaker.

Closes rust-lang#52629.

Remove obsolete flags in the i586_musl Dockerfile

Resolves an [outdated FIXME](https://github.com/rust-lang/rust/blob/ab8b961677ac5c74762dcea955aa0ff4d7fe4915/src/ci/docker/dist-i586-gnu-i586-i686-musl/Dockerfile#L45) in the Dockerfile for dist-i586-gnu-i586-i686-musl.

Cursor: update docs to clarify Cursor only works with in-memory buffers

Reduce misconceptions about Cursor being more general than it really is.

Fixes: rust-lang#52470

Do not suggest using `to_owned()` on `&str += &str`

 - Don't provide incorrect suggestion for `&str += &str` (fix rust-lang#52410)
 - On `&str + String` suggest `&str.to_owned() + &String` as a single suggestion

Fix color detection for Windows msys terminals.

Updates atty to pull in the fix softprops/atty#28.  Closes rust-lang/cargo#5724.

…matsakis

Use MultiSpan in E0707 and E709

…t, r=alexcrichton

Compile rustc before building tests for rustdoc

r? @alexcrichton

Don't use NonNull::dangling as sentinel value in Rc, Arc

Instead, rely on alignment and use usize::MAX as sentinel.

Cc rust-lang#52508

r? @joshtriplett

… r=cramertj

Forget Waker when cloning LocalWaker

Since NonNull is Copy the inner field of the cloned Waker was copied for
use in the new LocalWaker, however this left Waker to be dropped. Which
means that when cloning LocalWaker would also erroneously call drop_raw.

This change forgets the Waker, rather then dropping it, leaving the
inner field to be used by the returned LocalWaker.

Closes rust-lang#52629.

Simplify 2 functions in rustc_mir/dataflow

- `graphviz::outgoing`: the `enumerate` only provides indices; use a range instead
- `DataflowState::interpret_set`: change a push loop to an iterator and remove the `each_bit` helper function

…lacrum

Replace a few expect+format combos with unwrap_or_else+panic

That way the error strings won't be created if the related errors are not triggered.